Multiferroic BiFeO3 thin films have been extensively investigated because they have a very large remnant polarization and also exhibit the coexistence of ferroelectric and magnetic ordering. Wang J et al, 2003 Science 299, 1719. In bulk form, BiFeO3 is a rhombohedrally distorted perovskite structure with space group R3c, with a polarization P˜100 μC/cm2 along the [111] direction. Lebeugle D, Colson D, Forget A, and Viret M, 2007 Appl. Phys. Lett. 91, 022907. For most ferroelectric applications, high quality BiFeO3 thin films are required for fabrication of electronic devices. Such films are typically grown on single-crystal ceramic substrates. Such substrates have the disadvantages of expensive cost, rigidity and availability in only very limited sizes. It is desirable to be able to grow BiFeO3 films on very low-cost, wide-area, long-length, flexible substrates and still be able to manipulate the orientation and hence the polarization of the films.
Recently, the fabrication of three differently oriented, single-crystal, epitaxial BiFeO3 thin films was successfully accomplished via epitaxial growth on (111)-, (101)-, and (001)-oriented SrTiO3 substrates. Li J, Wang J, Wuttig M, Ramesh R, Wang N, Ruette B, Pyatakov A P, Zvezdin A K, and Viehland D, 2004 Appl. Phys. Lett. 84, 5261; Singh S K, Kim Y K, Funakubo H, and Ishiwara H, 2006 Appl. Phys. Lett. 88, 162904; Bea H, Bibes M, Zhu X-H, Fusil S, Bouzehouane K, Petit S, Kreisel J, and Barthelemy A, 2008 Appl. Phys. Lett. 93, 072901.
Growth of BiFeO3 films with different orientations was also reported on the Si substrates. This report demonstrated the growth of (110)- or (111)-oriented polycrystalline BiFeO3 on Si (001) substrates using different choices of barrier layers. Lee C C, Wu J M, and Hsiung C P, 2007 Appl. Phys. Lett. 90, 182909. A few groups have successfully deposited paraelectric/ferroelectric thin films on flexible metallic tapes. Dawley J T and Clem P G, 2002 Appl. Phys. Lett. 81, 3028; Ihlefeld J, Laughlin B, Hunt-Lowery A, Borland W, Kingon A, and Maria J-P, 2005 J. Electroceram. 14, 95; Kingon A I and Srinivasan S, 2005 Nat. Mater. 4, 233; Shin J, Goyal A, Jesse S, and Kim D H, 2009 Appl. Phys. Lett. 94, 252903.
The direct deposition of highly oriented perovskite-type BiFeO3 ferroelectric thin films on technologically important metallic substrates is complicated by the presence of an oxidizing growth environment at elevated temperature, which needs an oxygen diffusion barrier between ferroelectric films and metallic substrates. Moreover, there exists a large lattice mismatch between ferroelectric materials and metallic tapes.
Several techniques have been developed in the field of superconductors to fabricate wires or tapes wherein grain alignment is produced. Of particular note is the epitaxial growth of superconductors on such ordered substrates as the Rolling-Assisted-Biaxially-Textured-Substrates (RABiTS). RABiTS substrates typically include a textured metal underlayer (for example, nickel or nickel alloy) and an epitaxial buffer layer (for example, Y2O3 and/or yttria-stabilized zirconia, YSZ, and/or cerium oxide, CeO2). Epitaxial superconductors on biaxially-textured substrates have significantly improved critical current densities of high temperature superconductor tapes, and thus, improved suitability for commercial applications.